Harmonic lift drive system for a gantry conveyor

ABSTRACT

A gantry conveyor apparatus for transporting components between work stations in an assembly line. The apparatus includes an elevated gantry beam and two gantry carts movably mounted to roll along the beam. The gantry conveyor apparatus also includes a conveyor coupled to each gantry cart. The conveyor moves the carts along the gantry beam between stations in an assembly line. A lift tube is supported on each gantry cart and engages a part at one station, raises the part to an elevated transport position, and lowers and releases the part at a subsequent station. The apparatus also includes a harmonic lift drive coupled to the lift tubes and drives the lift tubes using a single motor rather than a separate motor at each lift.

CROSS-REFERENCE TO RELATED APPLICATIONS

Applicant claims the benefit of U.S. Provisional Application Ser. No.60/211,617, filed Jun. 14, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a gantry conveyor apparatus and, morespecifically, a gantry conveyor apparatus having multiple lift tubes.

2. Description of the Related Art

Gantry conveyor systems used in the manufacture and assembly ofautomotive vehicles are well known in the art. Gantry conveyor systemsare used as material handling devices to pick up components, such asvehicle frames, at one station and transport the components to asubsequent station along an assembly line. A gantry system generallycomprises an elevated gantry beam and a plurality of gantry cartsmovably mounted to roll along the beam between assembly line stations.Each gantry cart supports a lift tube assembly. The lift tube assembliesare each designed to pick up a part at a station then raise the partfrom the station to an elevated transport position. Once in thetransport position the attached part is carried by the gantry cart alongthe gantry beam to a position above a subsequent station along theassembly line. Once positioned above the subsequent station the lifttube lowers the attached part to the subsequent station and releases itthere. In the prior art, each lift tube assembly includes its owndedicated electric or hydraulic motor that raises and lowers the lifttube on that assembly. The inclusion of an electric or hydraulic motorto drive each lift tube assembly results in a relatively complex andcostly system.

FIG. 1 shows a typical prior art gantry system 10. Gantry legs 11 areused to support a gantry beam 12 above the shop floor. Typically, thegantry beam 12 is located 8 to 13 feet above the floor. Lift tubes 13are mounted on the gantry beam 12 and are powered by a motor 14 totranslate back and forth along the beam 12 to pickup and place parts atworkstations on the shop floor. As shown, the gantry system 10 wouldservice four workstations, one located beneath each of the lift tubes13, and one located to the right of the lift tube that is furthest righton the gantry beam 12. Tooling such as a component gripper (not shown)is attached to a mounting plate on the lower end of each lift tube 13.The tooling is used to secure a part for transfer from one workstationto the next. In hemming applications, the tooling may also be used tosecure a part in the hemming die for hemming. A separate motor (notshown) is provided for each of the lift tubes 13 to raise and lower thelift tubes.

Gantry systems are known to employ counterbalance systems to reduce theeffective load that the lift tube motors must lift. Some gantry systemsuse mechanical counterbalance weights. Other gantry systems use air(pneumatic) counterbalance systems. In each case, components of thecounterbalance system travel with each gantry cart. For example, in amechanical system, a counterbalance weight is coupled with each lifttube on each gantry cart.

In air counterbalance systems, a surge tank and a pneumaticcounterbalance cylinder travel with each cart. The purpose of each surgetank is to increase the volume capacity of the pressurized side of itsassociated pneumatic counterbalance cylinder. The increase in the volumecapacity reduces the pressure differential when a counterbalancecylinder is in different working positions. It's typical for the volumeof a surge tank in such a system to be 10 times the maximum volume ofits associated counterbalance cylinder. Each such air counterbalancesystem requires a feed line and an air regulator to supply air to makeup for any losses that may occur in the system because of leakyconnections and worn seals. Air counterbalance systems also have thedisadvantage that the pneumatic levels and flow rates in the variousparts of such systems are difficult to balance once the original factoryset balance has been altered.

It would be desirable to reduce the complexity and, the cost of gantryconveyor lift systems.

BRIEF SUMMARY OF THE INVENTION

The invention is embodied in a gantry conveyor apparatus fortransporting a plurality of components between workstations in anassembly line. The apparatus includes an elevated gantry beam and atleast two gantry carts movably mounted to roll along the beam. Theapparatus also includes a conveyor that is coupled to each gantry cartand is configured to move the carts along the gantry beam betweenstations in an assembly line. A lift is supported on each gantry cartand is configured to engage a part at one station, raise the part to anelevated transport position, and lower and release the part at asubsequent station.

The gantry conveyor apparatus also includes a harmonic lift drivecoupled to the lifts and configured to drive the lifts using a singlemotor. A gantry conveyor apparatus constructed according to theinvention is, therefore, able to move parts using a single lift motorrather than requiring a separate motor at each lift.

Objects, features and advantages of this invention include a harmonicdrive system for a gantry in which multiple lift tubes can be powered bya single motor, in which the cost of the gantry is reduced through theuse of a single lift drive for the entire gantry system; in which asimple mechanical or pneumatic counterbalance can be used; in which apassive lock-up is provided for the lift tubes in the raised positionwhile the gantry carts travel between work stations; and in which apassive lock-up can be designed to use the existing lower horizontalguide rail that guides the gantry carts.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

These and other objects, features and advantages of this invention willbe apparent from the following detailed description of the preferredembodiment(s) and best mode, appended claims, and accompanying drawingsin which:

FIG. 1 is an overhead perspective view of a prior art gantry system;

FIG. 2 is a side view of a gantry system constructed according to theinvention and showing lift tubes of the gantry system in a raisedposition;

FIG. 3 is a side view of the gantry system of FIG. 2 showing the lifttubes in a lowered position;

FIG. 4 is a side view of the gantry system of FIGS. 2 and 3 showing alift tube and a drive cart starting to advance to a work station;

FIG. 5 is a side view of the gantry system of FIGS. 2-4 showing a lifttube and drive cart between workstations;

FIG. 6 is a side view of the gantry system of FIGS. 2-4 showing the lifttube and drive cart of FIG. 5 entering a work station;

FIG. 7 is a side view of the gantry system of FIGS. 2-5 showing the lifttube and drive cart of FIGS. 5 and 6 after having arrived at the workstation;

FIG. 8 is a graphical representation of a front view of thereciprocating path of gantry lift tubes and tooling of the gantry systemof FIGS. 2-7;

FIG. 9 is a partial end view of the gantry system of FIGS. 2-7 showing agantry cart lift tube supported on the gantry beam;

FIG. 10 is a partial side view of a gantry system constructed accordingto a second embodiment of the invention and showing lower gantry cartguide rails used as lift tube support rails;

FIG. 11 is a side view of a mechanical counterbalance system installedin a gantry lift system constructed according to the invention;

FIG. 12 is a side view of an air counterbalance system installed in agantry lift system constructed according to the invention; and

FIG. 13 is a side view of a gantry system constructed according to theinvention and showing lift tubes of the gantry system in a raisedposition; and

FIG. 14 is a side view of the gantry system of FIG. 1 showing the lifttubes in a lowered position.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A gantry system 20 constructed according to the invention is shown inFIGS. 2-7. A gantry system 20′ constructed according to a secondembodiment of the invention is shown in FIG. 10 and a gantry system 20″constructed according to a third embodiment of the invention is shown inFIGS. 13 and 14. Reference numerals with the designation prime (′) inFIG. 10 and double-prime (″) in FIGS. 13 and 14 indicate alternativeconfigurations of elements that also appear in the first embodiment.Unless indicated otherwise, where a portion of the following descriptionuses a reference numeral to refer to the figures, I intend that portionof the description to apply equally to elements designated by primednumerals in FIG. 10 and double-primed numerals in FIGS. 13 and 14.

As with the prior art gantry system 10 shown in FIG. 1, a gantry system20 constructed according to the invention includes a stationary overheadgantry beam 23 and lift tubes 25 movably mounted on the gantry beam 23.A motor (not shown) is drivingly connected to the lift tubes 25 andlaterally translates the tubes 25 back and forth along the beam 23 totransport workpieces or parts between different workstations. Toolingsuch as a component gripper 26 is attached to a mounting plate 27 on thelower end of the lift tube 25. The tooling 26 is used to secure a partfor transfer from one workstation to the next. In hemming applications,the tooling 26 may also be used to secure a part in the hemming die forhemming. The lift tubes are also movably supported for generallyvertical reciprocal motion relative to the gantry beam 23 to allow thetubes to pick up parts for transport and to lower parts for placement.

Upper and lower guide rails 15 and 16 are mounted on a front face of thegantry beam 23, and support the gantry carts 18 for lateral motion alongthe gantry beam 23. A lift tube 25 is mounted on each gantry cart 18,and a mounting plate 27 on the bottom of each lift tube 25 receives thetooling 26 that is used to grip and carry a workpiece. Tie tubes 29couple together adjacent gantry carts 18 for movement along the gantrybeam 23.

FIG. 2 shows the lift tubes 25 in the raised position. The lift tubesare raised and lowered by a harmonic lift drive assembly 32. Theharmonic lift drive assembly 32 comprises a single electric motor andreducer gear combination 33 connected to the lift tubes by a lift drivelinkage. The lift drive linkage includes a drive arm 35, a drive link 37and drag link 44, multiple lift arms 39, lift rollers 41 and lift plates42 for each lift tube 25. The drive arm 35 is attached to an outputshaft 34 of the reducer gear. The drive arm 35 is pivoted to one end ofa drive link 37. In FIG. 2, the drive arm 35 and the drive link 37 areshown in a folded position. The other end of the drive link 37 ispivoted to the lever arm portion 38 of a lift arm 39. The lift arms 39are pivoted to lift arm supports 40 that are mounted on the gantry beam23. A lift roller 41 is mounted on the end of the each arm 39. The liftroller 41 engages the underside of a lift plate 42 that is attached tothe lift tube 25. The lift plate 42 is formed with beveled, lead-insections 43 on either side thereof.

The drive assembly 32 is able to actuate all the lift arms 39 by usingthe drag link 44 to tie the multiple lever arms 38 together. A supportroller 45 is mounted on each respective lift tube 25 in a position to beabove the level of a support rail 46 when the lift tube 25 is in theraised position. Gaps 47 are formed in the support rail 46 in verticalalignment with work stations to allow the lift tube support rollers 45to pass through the gaps 47 in the rail 46 so that the lift tubes 25 canbe lowered. The support rail 46 is mounted to the gantry beam by meansof support rail brackets 48.

FIG. 3 shows the lift tubes 25 in the lowered position. To lower thelift tubes, the motor-gear reducer 33 rotates the output shaft 34 andthe drive arm 35 until the drive arm 35 and the drive link 37 are in theextended position as shown. The motion of the drive link 37 to the rightrotates the lever arm portion 38 and lift arm 39 counterclockwise,lowering the lift roller 41. At the same time, the drag link 44 causesall of the lift arms 39 to undergo the same motion. This lowers all ofthe lift tubes 25 and the mounting plates 27 that the tooling 26 andworkpieces are attached to.

To raise the lift tubes, the motor and gear reducer 33 rotate the outputshaft 34 and the drive arm 35 so that the drive arm 35 and the drag link37 return to the folded position as shown in FIG. 2. The motion of thedrive link 37 to the left rotates the lever arm portion 38 and lift arm39 clockwise, raising the lift roller 41. This motion is tied to all ofthe lift arms by the drag link 44, and raises all of the lift tubes 25.

As the gantry carts transfer the lift tubes to the next workstation, thelift tube assemblies remain in the raised position as shown in FIG. 4.Before the lift plate 42 disengages from the lift roller 41, the supportroller 45 engages the support rail 46 to maintain the lift tube 25 in araised position. The lift support roller 45 maintains the lift tube inthe raised position as it travels to the next workstation.

As shown in FIG. 5, the support rail 46 supports the lift tube supportroller 45 while the gantry cart translates the lift tube 25 to the nextwork station, holding the lift tube 25 in the raised position.

As shown in FIG. 6, as the lift tube 25 approaches the next workstation,the lift roller 41 engages the tapered lead-in section 43 on theunderside of the lift plate 42. The lift roller 41 engages the lead-insection 43 of the lift plate 42 before the lift tube support roller 45reaches the gap in the support rail 46.

FIG. 7 shows the lift tube 25 at the next workstation. The lift roller41 is centered on the underside of the lift plate 42 to fully supportthe lift tube 25. The lift tube support roller 45 is centered over a gap47 in the support rail 46 so that the lift tube can be lowered topick-up or place a part in the work station.

As shown in FIG. 8, a lift tube 25 starts above the first workstation ata Start Position 1, and is then lowered to a Pickup Part Position 2. Innormal operation, the tooling 26 grips a part at the Pickup PartPosition 2 and then returns with the part to the Start Position 1 Thegantry cart then translates the lift tube 25, the tooling 26, and thepart to a Transfer Part Position 3, above the second workstation. Afterthe gantry cart reaches the Transfer Part Position 3 the lift tube,tooling 26 and part are lowered to a Release Part Position 4. Thetooling 26 releases the part at the Release Part Position 4 and then theempty tooling 26 is raised back to the Transfer Part Position 3. Thegantry cart then returns the lift tube to the Start Position 1. Thecycle then begins to repeat as the lift tube lowers to the Pickup PartPosition 2 to engage another part.

As shown in FIG. 9 the upper and lower guide rails 15, 16 are mounted onthe front face of the gantry beam 23. A roller 63 mounted on the gantrycart 18 rides on the upper rail 15 to support the gantry cart and lifttube on the gantry beam. Upper guide bearings 64 mounted on the gantrycart 18 maintain the roller centered on the upper rail 15. Lower guidebearings 66 mounted on the gantry cart 18 engage both sides of the lowerguide rail 16 to provide stability for the gantry cart and lift tube 25.

In the second embodiment of the system shown in FIG. 10, a lower gantryguide rail 16′ is used as the support rail for a lift tube supportroller 70. Gaps 71 in the lower gantry cart guide rail 16′ correspond tothe position of the lift tube support roller 70 when the lift tube 25′is at a work station and allow the support roller 70 to pass through thecart rail 16′ so that the lift tube 25′ can be lowered. The supportroller 70 rides on the lower gantry cart guide rail 16′ while the gantrycart is transferring from one workstation to the next. This constructionallows the elimination of separate support rails 46 and the associatedsupport brackets 48 as shown in FIGS. 2-7, 9,11 and 12. This embodimentincludes guide bearings (not shown) that support the gantry cart 18′ oneither side of the gap 71 to prevent the gantry cart 18′ from cocking atthe workstations.

According to the invention, one lift drive assembly 32 is required foran entire gantry system, and one lift arm 39 and lift arm support 40 isrequired at each workstation. The lift drive system 32 is not limited toa motor and gear reducer with a crank arm as shown. The drive systemcould comprise any other suitable drive system such as a single drivecylinder powered with air or hydraulic fluid, a servo driven rack andpinion, or a ball screw.

One advantage of a harmonic lift drive system constructed according tothe invention is that the whole system can be mechanicallycounterbalanced through the use of a counterweight that is coupled tothe lift drive linkage and positioned to reduce the effective loading onthe motor by offsetting the weight of parts supported by the lifts. Thesystem can also be counterbalanced with a single air counterbalancecylinder attached to the drag link 44.

FIG. 11 shows a mechanical counterbalance system 49 in which acounterbalance weight 50 is attached to a counterbalance arm 51 thatextends from a harmonic lift arm 39. The value of the counterbalanceweight is computed by adding the total weight of the lift tubes and anylift tube tooling 26 to one half the total weight of a typical loadcarried by the gantry system. This sum is known as the effective load.The effective load is then multiplied by the length of the lift arm 39,and divided by the length of the counterbalance arm. This computationprovides the total counterbalance weight. The value of eachcounterbalance weight to be mounted on each counterbalance arm is thencomputed by dividing the total counterbalance weight by the number oflift arm assemblies.

The mechanical counterbalance system 49 shown in FIG. 11 uses acounterweight 50 on the end of each counterbalance arm 51. The purposeof the counterbalance system is to reduce the effective load that themotor and gear reducer 33 must lift. An advantage of this type ofcounterbalance system is that evenly distributing the counterweights 50among the lifter assemblies minimizes the load transferred through thedrag link 44. Another advantage is that a mechanical counterbalancesystem requires very little maintenance. This is because, once thecounterbalance weights are in place, they do not require service orfurther adjustments.

FIG. 12 shows a pneumatic counterbalance system 55 used with theharmonic lift tube system of the present invention. A pneumaticcounterbalance system has the advantage that one cylinder 56 is used tocounterbalance the whole drive system. One end 57 of the cylinder 56 ispivotally mounted to a bracket 58 that is mounted to the gantry beam 23.A rod 59 that extends from the rod end 60 of the cylinder is pivotallymounted to an extension 61 of the lift arm 39. Since, in thisarrangement, the counterbalance load is transmitted through the draglink 44; the drag link must be appropriately sized. In the embodimentshown, the rod end 60 of the cylinder is pressurized, while the otherend is vented to atmosphere, so that the pressure in the system pullsthe rod 59 into the cylinder 56. Unlike prior art pneumaticcounterbalance systems, the cylinder 56 does not travel with the gantrycart, and as a result, the surge tank (not shown) can be mounted on thegantry beam 23 in a stationary position. Additionally, the mass of thecylinder 56 and the rod 59 is less than the mass of mechanicalcounterbalance weights 50 shown in FIG. 11, and as a result, thepneumatic counterbalanced system has less mass to move than amechanically counterbalanced system.

As shown in FIGS. 13 and 14, in the third embodiment of the gantryconveyor apparatus, the motor 14″ is supported stationary relative to agantry beam 12″ and is drivingly coupled to a plurality of lifts 25″through a lift drive linkage as in the first and second embodiments.Also similar to the first two embodiments, the lift drive linkagecomprises a harmonic drive arm 35″ that is pivotally coupled to a drivelink 37″ that is pivotally coupled to a plurality of lift arms 39″through a series of drag links 44″. However, unlike the first and secondembodiments, in the apparatus of FIGS. 13 and 14 the lift arms 39″drivingly engage a generally horizontal lift rail 72 in a parallelmanner. The lift arms 39″ drive the lift rail 72 through reciprocalvertical motion. The lifts 25″ are supported on respective rollers 74 onthe lift rail 72 and are supported on the lift rail 72 for simultaneousreciprocal vertical movement with the lift rail. The lift arms 39″engage the lift rail 72 in a parallel manner such that simultaneousreciprocal rotational lift arm motion alternately raises and lowers thelift rail 72 in a generally horizontal attitude. Because the lift rail72 supports the lifts 25″ for vertical reciprocal movement, theembodiment of FIGS. 13 and 14 does not require a support rail 46 tosupport the lifts in their raised positions. In addition, the lift railreduces the number of lift arms necessary to raise and lower the lifts.

This description is intended to illustrate certain embodiments of theinvention rather than to limit the invention. Therefore, it usesdescriptive rather than limiting words. Obviously, it's possible tomodify this invention from what the description teaches. Within thescope of the claims, one may practice the invention other than asdescribed.

What is claimed is:
 1. A gantry conveyor apparatus for transporting aplurality of components between work stations in an assembly line, theapparatus comprising: a stationary elevated gantry beam; at least twogantry carts movably mounted to roll along the beam; a conveyor coupledto each gantry cart and configured to move the carts along the gantrybeam between stations in an assembly line; a lift supported on eachgantry cart and configured to engage a part at one station, raise thepart to an elevated transport position, and lower and release the partat a subsequent station; and a harmonic lift drive coupled to the liftsand configured to drive the lifts using a single motor.
 2. A gantryconveyor apparatus as defined in claim 1 in which the single motor issupported stationary relative to the gantry beam and is coupled to thelifts through a lift drive linkage comprising a harmonic drive arm and adrive link, the drive link being coupled directly to a first lift armand through a drag link to an additional lift arm, each lift armengaging a lift such that rotation of the lift arm raises respectivelifts.
 3. A gantry conveyor apparatus as defined in claim 2 in which thedrive link is coupled directly to a first lift arm and through a seriesof drag links to additional lift arms, each lift arm engaging a liftsuch that rotation of the lift arms raises and lowers the respectivelifts.
 4. A gantry conveyor apparatus as defined in claim 1 in which:the apparatus includes a plurality of gantry carts movably mounted toroll along the beam; the conveyor is coupled with each cart of theplurality of gantry carts and is configured to move each cart of theplurality of carts along the gantry beam between assembly line stations;and a lift is supported on each gantry cart and is configured to engagea part at one station, raise the part to an elevated transport position,and lower and release the part at a subsequent station.
 5. A gantryconveyor apparatus as defined in claim 1 in which: the motor issupported stationary relative to the gantry beam; the motor is drivinglycoupled to the lifts through a lift drive linkage; the lift drivelinkage comprises a harmonic drive arm coupled to a drive link; thedrive link is coupled to a first lift arm; the first lift arm drivinglyengages a generally horizontal lift rail and is configured to drive thelift rail through reciprocal vertical motion; and the lifts aresupported on the lift rail for simultaneous reciprocal verticalmovement.
 6. A gantry conveyor apparatus as defined in claim 5 in which:the drive link is coupled through a drag link to an additional lift arm;and the first lift arm and the additional lift arm engage the lift railsuch that lift arm motion alternately raises and lowers the lift rail.7. A gantry conveyor apparatus as defined in claim 5 in which the drivelink is coupled through a series of drag links to a plurality ofadditional lift arms; and the lift arms engage the lift rail in aparallel manner such that motion of the lift arms alternately raises andlowers the lift rail.
 8. A gantry conveyor apparatus as defined in claim1 in which the harmonic lift drive includes a counterbalance coupled tothe lift drive system and configured to reduce effective loading on themotor by providing a counterbalance load to offset the weight of partsattached to the lifts.
 9. A gantry conveyor apparatus as defined inclaim 8 in which the counterbalance includes a counterbalance weightcoupled to the lift drive linkage such that a counterbalance loadprovided by the weight is transmitted through the drive linkage to morethan one lift.
 10. A gantry conveyor apparatus as defined in claim 9 inwhich the counterbalance includes only a single weight that is supportedon a counterbalance arm that extends from one of the lift arms.
 11. Agantry conveyor apparatus as defined in claim 8 in which thecounterbalance includes an air counterbalance cylinder coupled to thelift drive linkage such that a counterbalance load provided by thecylinder is transmitted through the drive linkage to more than one lift.12. A gantry conveyor apparatus as defined in claim 11 in which one endof the cylinder is connected to the stationary gantry beam and anopposite end of the cylinder is connected to the lift drive linkage. 13.A gantry conveyor apparatus as defined in claim 11 in which thecounterbalance includes a stationary surge tank connected to thecylinder and configured to increase the volume capacity of a pressurizedside of the cylinders.
 14. A gantry conveyor apparatus as defined inclaim 1 in which the apparatus includes a passive lock-up configured tohold the lifts in the raised position while the gantry carts travelbetween work stations and to release the lifts for lowering when thegantry carts are at work stations.
 15. A gantry conveyor apparatus asdefined in claim 14 in which the passive lockup includes a lowerhorizontal guide rail of the gantry beam and is configured to supportthe gantry carts by engaging gantry cart rollers between work stations,the separate guard rail having gaps at the work stations where the guardrail does not support the cart roller.
 16. A gantry conveyor apparatusas defined in claim 14 in which the passive lock-up includes a separateguard rail spaced from and supported parallel to the gantry beam andconfigured to support the gantry carts by engaging gantry cart rollersbetween work stations, the separate guard rail having gaps at the workstations where the guard rail does not support the cart roller.